Disproportionation of chloroper-fluoropropenes



United States Patent fiice 3,081,358 Patented Mar. 12, 1963 Thisinvention relates to manufacture of perhalopropenes and moreparticularly to production of 1,1-dichlorotetrafluoropropene 1', andhexafluoropropene a known commercial monomer.

The chloropentafluoropropenes containing fluorine in the 2 position,i.e. l chloropentafluoropropene 1 (CF CF:CFCI, B.P. 7.8 C.) and3-chloropentafluoropropene-l (CF CICF:CF HP. 7.6 C.), because of thefluorine content in the first and third positions and the presence ofonly a single chlorine in the molecule, afford notably suitable startingmaterials for manufacture of hexafliuoropropene if an economical processwere available.

Contrary to expectation, it has been found that both of the startingmaterials mentioned may be disproportionated to CF CF:CF B.P. minus 29.4C. and to CF CF:CCI B.P. plus 46.4 C. While disproportionation ofchlorofluoromethanes and ethanes is known, prior art teaches thatdisproportionation of a chlorofluoropropene occurs only in the allylicposition. Hence, it would not be anticipated that CF CF:CFCl could bedisproportionated since the allylic position (trihalomethyl) is alreadyfilled with fluorine. Sensitivity of CF CICRCF to isomerization to CFCRCFCI is known. Thus, it would be expected that attempts todisproportionate CF clCFzcF would fail because of conversion of CFCICF:CF to CF CF:CFCl which, for reasons just noted, is theoreticallynon-disproportionatable.

A major object of this invention is to provide a relatively simplemethod for disproportionating CF CRCFCI and CF CICF :CF to make CF CF:CFand CF CF :CCl

In accordance with the invention it has been found that certain solidaluminum fluoride (AlF materials possess the properties of effectivelydisproportionating phase, solid catalytic procedure by which the desireddisproportionation products, CFgCFICFg and may be made in good yields.Opposed to expectancy as based on prior art knowledge, it has been foundthat the catalytic material disclosed herein not only disproportionatesboth starting materials mentioned but also efiects disproportionation ofthe two different starting materials to the same products.

Different types of aluminum fluorides are known. In general thesematerials are composed of A1F crystals of relatively large size, i.e.not less than 1000 and usually several thousand Angstrom units radiusand above, as in the case of commercial types of AlF available on themarket. The aluminum fluoride catalysts utilized in accordance with thepresent invention are of noncrystalline or amorphous structure, and whenexamined by X-ray diffraction technique show extremely small orsub-microscopic crystals designated as crystallites. These aluminumfluorides are of crystallite size not greater than about 500 Angstromunits radius and are derived by reaction of aluminum chloride and HF. Ascrystallite size decreases, catalytic activity increases, and thepreferred aluminum fluorides are those having crystallite size of about200' A and below, as determined by X-ray diffraction technique.Catalytic aluminum fluorides of this type are more fully discussed inU.S.P. 2,676,996 of April 27, 1954 which discloses processes for makingthe same by procedures involving reaction of aluminum chloride and HF.

Practice of the invention comprises subjecting or CF ClCFzCF or mixturesof the same to heating at substantially elevated temperatures in thepresence of the herein described aluminum fluoride catalyst for a timesufficient to disproportionate a substantial amount of the startingmaterial, and recovering, from the resulting reaction mixture,- eitheror both of CF CF:CF and The reactions involved may be represented by thefollowing:

In accordance with the invention, it has been found thatdisproportionation, with formation of appreciable quantities of CF CRCFand CF CF :CC1 significantly takes place at temperature of about 300 C.Preferred low temperature for commercially acceptable yields is about325 C. Temperatures as high as above 450 C. may be utilized withoutinterferingwith yields, although appreciably higher temperaturesdesirably should be avoided to prevent deactivation of catalyst andminimize breakdown of the organic materials. Operating temperatureshigher than about 425 C. appear to afford no significant operatingadvantages. Hence, preferred temperature lie substantially in the rangeof 325-425 C.

Contact time may be varied considerably without noticeable disadvantageto process efficiency. Increasing contact time and reactor temperatureresult in higher conversion of starting materials to'sought-forproducts, and lower contact time and reactor temperature result in lowerconversion. In general, contact time may lie in the range of 2 to 50seconds and preferably in the range of 5 to 30 seconds. To asubstantialextent, contact time and reaction temperature areinterrelated, and for any given operation optimum conditions may bedetermined by test runs.

'In general practice, starting material is metered in vapor form into atubular reactor, packed with the crystallite aluminum fluoride catalyst,made of suitable inert material such as nickel, and provided withexternal heating equipment preferably including automatic means formaintaining given temperatures in the reaction zone. Product recoverymay be effected more or less conventionally as in this art. For example,reactor exit gases may be passed into a trap cooled to about minus 78 C.by a Dry Ice-acetone mixture. In this trap, the reaction products CFCF:CF and CF CF:CCl and also any unreacted chloropentafluoropropenestarting materials are condensed. Separation and recovery of individualcompounds may be effected by conventional fractional distillation. Ifdesired, the A11 catalyst exit may be passed directly into a waterscrubber to remove trace amounts of any acid vapors which may haveformed in the reaction. In this instance, any organic condensate formedin the scrubber may be separated from the water layer, dried andcombined with the organic condensate of the cold trap for distillation.I

Hexafluoropropene is a known commercial monomer. The CF CF:CCl productis useful per se as a co-monowhich tend to poison catalysts.

mer. However, CF CF:CCl can be readily reconverted to CF CF:CFClstarting material by the reactions Antimony pentachloride CatalystCFQGFCLCFOIZ Zn CFsOFZCFCl ZnOlz Hence, if so desired the invention maybe utilized to yield hexafluoropropene exclusively by reconversion of CFCF CC1 to CF CF CFCl.

Where the starting material is 3-chloropentafluoropro pene, CF Cl.CF:CFit is noted that reaction according to the invention procedure givesrise to some isomerization to the CF CFzCFCl. Such isomerization doesnot influence the net result, since the normal recycle of unreacted CFCLCRCF and isomer CF CF:CFCl efiects disproportionation to the sameproducts.

Any decline of activity of the aluminum fluoride catalyst during longuse may be completely restored by treatment with oxygen gas attemperatures of about 400-5 C. Time of such treatment may vary from 4 to8 hours as needed. In many operations it may be desirable to protect thecatalyst from decline in activity during long runs. Such protection maybe effected by passing incoming reactants over activated carbon held atsuitable elevated temperatures which may be in the range of 175- 450 C.Pretreatment of this nature removes from incoming halocarbons certainunknown types of impurities In the lower portion of the statedtemperature range, activated carbon is inert, other than as a purifier,as shown by Example 4. As indicated by Example 2, at higher portions ofsuch range, any incoming CF ClCF :F is isomerized to CF CF:CFC1 to suchan extent that most of the C F Cl exiting the carbon pretreater is CFCFzCFCl.

The reactions described may be carried out at substantially atmosphericpressure. Usually, in large scale operation plus pressure of 2-0p.s.i.g. is used to maintain gas flow thru the apparatus train. Suborsuper-atmospheres afford no operating advantages.

In the following examples the anhydrous aluminum fluoride catalystemployed had a crystallite size below about 200 Angstrom units radiusand had been prepared by procedure substantially the same as in ExampleC of U.S.P. 2,676,996.

Example 1.'Ihis example illustrates preparation of hexafluoropropene and1,1-dichlorotetrafluoropropene-l by disproportionation of3-chloropentafluoropropene-1. Incoming CF ClCF:CF was subjected to acarbon pretreatment. In this particular operation, the carbon was inertwith regard to disproportionation, the carbon functioning only to removecertain not understood types of impurity from the incoming organic, andthus enhancing longevity of the disproportionating catalyst, i.e. thecrystallite aluminum fluoride. The apparatus system included apretreater and a reactor connected in series. The pretreater and thereactor were each a nickel tube 1' ID. and 36" long, and each wasenveloped substantially throughout its length by an electrical heatingunit. The exit of the reactor was connected to a condensing trap cooledto about minus 78 C. by a Dry Ice-acetone mixture. The pretreater wasfilled with 0.438 liter (175 g.) of Columbia 6G activated carbon ofabout 8-14 mesh, and the reactor was filled with about 0.438 liter (438g.) of the crystallite aluminum fluoride catalyst. Throughout the run,the carbon pretreater was maintained at temperatures in the range ofabout 170232 C., averaging about 220 C., and temperature in the reactorwas held in the range of about 374399 C., averaging about 395 C. Duringa period of 4.3 hours, about 1177 g. (7.1 mols) of CF ClcFzCF were fedas vapor into the inlet of the carbon pretreater. Passage of gases thruthe system were such that contact time in the aluminum fluoride reactorwas about 20 seconds. The exit gases of the aluminum fluoride reactorwere condensed in the Dry Iceacetone trap, and about 1128 g. ofcondensate were re- I: covered. On fractional distillation of theorganic condensate, there were recovered about 321 g. (2.14 mols) of CFCF=CF representing about 30 mol percent yield based on the mols ofstarting material fed; 390 g. (2.13 mols) of CF CF:CCl representingabout a 30 mol percent yield; and 390 g. (2.13 mols) of CF CF:CFClrepresenting a 30 mol percent yield. Conversion (mols of startingmaterial consumed divided by mols of starting material fed andmultiplied by was about 60 mol percent. Following Example 4 shows thattreatment of CF CICRCF with activated carbon at temperatures below about195220 C. does not efifect disproportionation of CF ClCF=CF to CF CF:CFor CF CF:CCl Hence, it will be understood that the activated carbon inthe instant example takes no part in the disproportionation reaction,and that the disproportionation demonstrated is effected entirely by thealuminum fluoride catalyst.

Example 2.This run illustrates isomerization of CF CICROF to CF CF:CFClby subjecting the former to the action of activated carbon at relativelyhigh temperatures, and shows that under these temperature conditionsthere is very little disproportionation of to CF CF :CF and CF CF zCClThe single reactor employed with a 1" LD. nickel tube about 36 long, andenveloped substantially throughout its length with an electrical heatingunit. Exit of the reactor was connected to a Dry Ice-acetone trap. Thereactor was filled with 0.438 liter g.) of Columbia 6G activated carbonof about 8-14 mesh. Throughout the run the temperature in the reactorwas maintained in the rangeof about 426-452 C. averaging about 450 C.Over a period of about 4.5 hrs., about 1420 g. (8.52 mols) of CF CICRCFcontaminated with little CF CF:CFCl was passed into the carbon reactor.Contact time was about 20 seconds. The exit gases were condensed andcollected in the trap, and about 1273 g. of condensate were collected.On fractional distillation of the organic condensate there wererecovered about 100 g. (0.67 mol) of CF CF:CF representing about 7.7 molpercent yield based on the starting material fed; 1156 g. (6.91 mols) ofl-chloropentafluoropropene-l CF OF:CFCl representing about 81.3 molpercent yield; and 54 g. (0.30 mol) of CF CF:CCl representing about 3.6mol percent yield. Conversion (same basis as Example 1) of the cFClCFzC-F starting material was about 92%. This example demonstrates thatactivated carbon at about 450 C. disproportionates CF ClCF:CF to only anotably minor extent.

Example 3.The apparatus employed was the same as in Example 1. During a10 /2 hr. portion of a 128 hr. run, 1685 g. (10.2 mols) of CF ClCF:CFwere passed into and thru the pretreater-reactor system. During this 10hr. period, temperature in the carbon pretreater was maintained at about400 C. and the aluminum fluoride catalyst in the reactor was maintainedat a temperature of about 325 C. Contact time in the AlF reactor wasabout 40 seconds. The exit gases of the aluminum fluoride catalystreactor were handled substantially as before, and 1119 g. of organiccondensate were recovered. On fractional distillation of the recoveredcondensate there were recovered 426 g. (2.84 mols) of perfluoropropenerepresenting 42 mol percent of the total mols of the recovered organiccondensate; 192 g. (1.15 mols) of a mixture of CF CICRCF and CF CF:CFClrepresenting 17 mol percent of the condensate; and 501 g. (2.74 mols) ofCF CF :CC1 representing 40 mol percent of the condensate. Since Example2 demonstrates that, in Example 3, the C F Cl entering the aluminumfluoride reactor was roughly 90% CF CF:CFCl, it will be understood thatExample 3 demonstrates the eflectiveness of the aluminum fluoridecatalyst for disproportionating CF CF:CFCl to perfluoropropene and CFCF:CCl

Example 4.In this run, the single reactor employed was a 1'' ID. nickeltube enveloped substantially throughout its length with an electricalheating unit. Reactor was filled with 0.438 liter (175 g.) of Columbia6G activated carbon of about 8-14 mesh. Throughout the run, temperaturein the reactor was maintained in the range of about 195220.3-chloropentafluoropropene-1 was passed into and thru the reactor at arate of about 1 moi/hr. The exit gas of the reactor was subjected to gaschromatography and was shown by infrared absorption spectra to beidentical with the starting material. This run demonstrates thatactivated carbon at the temperature indicated is inert with respect todisproportionating or otherwise affecting CF ClCF CF We claim:

1. The process which comprises heating starting material of the groupconsisting of CF CICRCF and CF CF:CFCl to temperatures substantially inthe range of 300450 C., in the presence of anhydrous aluminum fluoridecatalyst and for a time suflicient to disproportionate a substantialamount of said starting material, said catalyst having crystallite sizenot substantially greater than 500 Angstrom units radius and having beenderived by reaction of aluminum chloride and HF, and recovering, fromthe resulting reaction mixture, material of the group consisting of CFCF:CF and CF CF:CCI

2. The process of claim 1 in which temperature is substantially in therange of 325-425 C.

3. The process for making CF CFzCF which comprises heating startingmaterial of the group consisting of CF CICRCF and CF CF:CFCl totemperatures substantially in the range of 32542S C. in the presence ofanhydrous aluminum fluoride catalyst for a time suflicient todisproportionate a substantial amount of said starting material, saidcatalyst having crystallite size not substantially greater than 500Angstrom units radius and having been derived by reaction of aluminumchloride and HF, and recovering CF CRCF from the resulting reactionmixture.

6. The process for making CF CF:CF which com-- prises heating CFgClCFzCFto temperature substantially in the range of 325-425 C. in the presenceof anhydrous aluminum fluoride catalyst for a time suflicient todisproportionate a substantial amount of said starting material, saidcatalyst having crystallite size not substantially greater than 500Angstrom units radius and having been derived by reaction of aluminumchloride and HF, and recovering CF CF:CF from the resulting reactionmixture.

7. The process for making CF CF:CF which comprises heating CF CF:CFCI totemperatures substantially in the range of 325425 C. in the presence ofanhydrous aluminum fluoride catalyst for a time suflicient todisproportionate a substantial amount of said starting material, saidcatalyst having crystallite size not substantially greater than 500Angstrom units radius and having been derived by reaction of aluminumchloride and HF, and recovering CF CF:CF from the resulting reactionmixture.

References Cited in the file of this patent UNITED STATES PATENTS2,478,201 Miller et al. Aug. 9, 1949 2,478,932 Miller Aug. 16, 19492,637,748 Miller May 5, 1953 2,676,996 Miller et a1. Apr. 27, 19542,767,227 Calfee et a1. Oct. 16, 1956 OTHER REFERENCES Prober, I.A.C.S.76 pp. 4189-4191 (1954).

1. THE PROCESS WHICH COMPRISES HEATING STARTING MATERIAL OF THE TERIALOF THE GROUP CONSISTING OF CF2CICF:CF2 AND CF3CF:CFCI TO TEMPERATURESSUBSTANTIALLY IN THE RANGE OF 300-450* C., IN THE PRESENCE OF ANHYDROUSALUMINUM FLUORIDE CATALYST AND FOR A TIME SUFFICIENT TO DISPROPORTIONATEA SUBSTANTIAL AMOUNT OF SAID STARTING MATERIAL, SAID CATALYST HAVINGCRYSTALLITE SIZE NOT SUBSTANTIALLY GREATER THAN 500 ANGSTROM UNITSRADIUS AND HAVING BEEN DERIVED BY REACTION OF ALUMINUM CHLORIDE AND HF,AND RECOVERING, FROM THE RESULTING REACTION MIXTURE, MATERIAL OF THEGROUP CONSISTING OF CF3CF:CF2 AND CF3CF:CCI2.